Measurement of fusion evaporation residue cross sections in the Ti48+Ba138 reaction

Evaporation residue cross sections are measured for the reaction $^{48}\mathrm{Ti}+^{138}\mathrm{Ba}$ which forms the compound nucleus ${}^{186}{\mathrm{Pt}}^{*}$. The cross sections are measured at beam energies in the range of 189.3--234.4 MeV. The experimental evaporation residue cross sections are compared with the dynamical model which employs one-dimensional Langevin dynamical calculations. The dissipation strength of the Langevin equation is calculated using both chaos weighted wall formula and a constant reduced dissipation function. The measured ER cross sections are found to be much less than the theoretical predictions. Further, the measured ER cross sections for the system $^{48}\mathrm{Ti}+^{138}\mathrm{Ba}$ are compared with those of $^{32}\mathrm{S}+^{154}\mathrm{Sm}$ forming the same compound nucleus. The suppression in the evaporation residue cross sections of the former reaction may be attributed to the increasing competition from quasifission. The quasifission reaction is found to have superseded any effect of neutron shell closure $(N=82)$ of the target in the present study.